U.S. patent number 8,958,051 [Application Number 13/335,129] was granted by the patent office on 2015-02-17 for lithographic apparatus, device manufacturing method and apparatus for de-gassing a liquid.
This patent grant is currently assigned to ASML Netherlands B.V.. The grantee listed for this patent is Jurgen Benischek, Roelof Frederick De Graaf, Johannes Henricus Wilhelmus Jacobs, Franciscus Johannes Herman Maria Teunissen, Martinus Cornelis Maria Verhagen. Invention is credited to Jurgen Benischek, Roelof Frederick De Graaf, Johannes Henricus Wilhelmus Jacobs, Franciscus Johannes Herman Maria Teunissen, Martinus Cornelis Maria Verhagen.
United States Patent |
8,958,051 |
Verhagen , et al. |
February 17, 2015 |
Lithographic apparatus, device manufacturing method and apparatus
for de-gassing a liquid
Abstract
An apparatus configured to de-gas a liquid includes a
semi-permeable membrane having a first side on which the liquid is
provided; and (i) a vaporizer configured to provide vapor of the
liquid to a second side of the membrane; or (ii) a gas inlet
configured to provide a gas to the second side of the membrane, the
gas adapted to dissociate when dissolved in the liquid and an ion
exchanger for the liquid downstream of the semi-permeable
membrane.
Inventors: |
Verhagen; Martinus Cornelis
Maria (Valkenswaard, NL), De Graaf; Roelof
Frederick (Veldhoven, NL), Jacobs; Johannes Henricus
Wilhelmus (Eindhoven, NL), Teunissen; Franciscus
Johannes Herman Maria (Rotterdam, NL), Benischek;
Jurgen (Geldrop, NL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Verhagen; Martinus Cornelis Maria
De Graaf; Roelof Frederick
Jacobs; Johannes Henricus Wilhelmus
Teunissen; Franciscus Johannes Herman Maria
Benischek; Jurgen |
Valkenswaard
Veldhoven
Eindhoven
Rotterdam
Geldrop |
N/A
N/A
N/A
N/A
N/A |
NL
NL
NL
NL
NL |
|
|
Assignee: |
ASML Netherlands B.V.
(Veldhoven, NL)
|
Family
ID: |
36931656 |
Appl.
No.: |
13/335,129 |
Filed: |
December 22, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120097034 A1 |
Apr 26, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12198448 |
Jan 31, 2012 |
8107053 |
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11067492 |
Feb 28, 2005 |
7428038 |
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Current U.S.
Class: |
355/30;
355/53 |
Current CPC
Class: |
G03F
7/70341 (20130101) |
Current International
Class: |
G03B
27/52 (20060101); G03B 27/42 (20060101) |
Field of
Search: |
;355/30,53 ;250/548 |
References Cited
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|
Primary Examiner: Nguyen; Hung Henry
Attorney, Agent or Firm: Pillsbury Winthrop Shaw Pittman
LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent Ser. No.
12/198,448, filed Aug. 26, 2008, which issued as U.S. Pat. No.
8,107,053 on Jan. 31, 2012, which is a continuation of U.S. patent
Ser. No. 11/067,492, filed Feb. 28, 2005, now U.S. Pat. No.
7,428,038, the content of which are incorporated herein in their
entirety by reference.
Claims
The invention claimed is:
1. An apparatus configured to de-gas a liquid, the apparatus
comprising: a semi-permeable membrane having a first side on which
the liquid is provided; and (i) a vaporizer configured to provide
vapor of the liquid to a second side of the membrane; or (ii) a gas
inlet configured to provide a gas to the second side of the
membrane at a pressure substantially equal to or lower than one
atmosphere, the gas adapted to dissociate when dissolved in the
liquid, wherein the gas is carbon dioxide.
2. The apparatus of claim 1, wherein the pressure is less than 0.5
atmosphere.
3. The apparatus of claim 2, wherein the pressure is less than 0.05
atmosphere.
4. The apparatus of claim 1, wherein the gas dissociates into ions
when dissolved in the liquid, the apparatus further comprising an
ion exchanger configured to remove said ions from the liquid.
5. The apparatus of claim 1, wherein a gas concentration in the
liquid downstream of the membrane is less than about 200 parts per
billion.
6. The apparatus of claim 1, wherein the membrane includes a
plurality of tubes.
7. An apparatus configured to de-gas a liquid, the apparatus
comprising: a semi-permeable membrane having a first side on which
the liquid is provided; and (i) a vaporizer configured to provide
vapor of the liquid to a second side of the membrane; or (ii) a gas
inlet configured to provide carbon dioxide to the second side of
the membrane.
8. The apparatus of claim 7, wherein carbon dioxide is at a
pressure substantially equal to or lower than one atmosphere.
9. The apparatus of claim 8, wherein the pressure is less than 0.5
atmosphere.
10. The apparatus of claim 9, wherein the pressure is less than
0.05 atmosphere.
11. The apparatus of claim 7, comprising an ion exchanger
configured to remove ions from the liquid, said ions resulting from
the dissociation of carbon dioxide in the liquid.
12. A lithographic apparatus comprising: an apparatus configured to
de-gas a liquid, the apparatus comprising: a semi-permeable
membrane having a first side on which the liquid is provided; and
(i) a vaporizer configured to provide vapor of the liquid to a
second side of the membrane; or (ii) a gas inlet configured to
provide a gas to the second side of the membrane at a pressure
substantially equal to or lower than one atmosphere, the gas
adapted to dissociate when dissolved in the liquid; and a liquid
confinement structure configured to confine the de-gassed liquid in
a space between a substrate and a projection system configured to
project a radiation beam onto the substrate such that the radiation
beam will pass through the de-gassed liquid.
13. The apparatus of claim 12, wherein the gas is carbon
dioxide.
14. The apparatus of claim 12, wherein the pressure is less than
0.5 atmosphere.
15. The apparatus of claim 12, wherein the gas dissociates into
ions when dissolved in the liquid, the apparatus further comprising
an ion exchanger configured to remove said ions from the
liquid.
16. A lithographic apparatus comprising: an apparatus configured to
de-gas a liquid, the apparatus comprising: a semi-permeable
membrane having a first side on which the liquid is provided; and
(i) a vaporizer configured to provide vapor of the liquid to a
second side of the membrane; or (ii) a gas inlet configured to
provide carbon dioxide to the second side of the membrane; and a
liquid confinement structure configured to confine the de-gassed
liquid in a space between a substrate and a projection system
configured to project a radiation beam onto the substrate such that
the radiation beam will pass through the de-gassed liquid.
17. The apparatus of claim 16, wherein carbon dioxide is at a
pressure substantially equal to or lower than one atmosphere.
18. The apparatus of claim 17, wherein the pressure is less than
0.5 atmosphere.
19. The apparatus of claim 16, comprising an ion exchanger
configured to remove ions from the liquid, said ions resulting from
the dissociation of carbon dioxide in the liquid.
Description
FIELD
The present invention relates to a lithographic apparatus and a
method for manufacturing a device and an apparatus for de-gassing a
liquid.
BACKGROUND
A lithographic apparatus is a machine that applies a desired
pattern onto a substrate, usually onto a target portion of the
substrate. A lithographic apparatus can be used, for example, in
the manufacture of integrated circuits (ICs). In that instance, a
patterning device, which is alternatively referred to as a mask or
a reticle, may be used to generate a circuit pattern to be formed
on an individual layer of the IC. This pattern can be transferred
onto a target portion (e.g. comprising part of, one, or several
dies) on a substrate (e.g. a silicon wafer). Transfer of the
pattern is typically via imaging onto a layer of
radiation-sensitive material (resist) provided on the substrate. In
general, a single substrate will contain a network of adjacent
target portions that are successively patterned. Known lithographic
apparatus include so-called steppers, in which each target portion
is irradiated by exposing an entire pattern onto the target portion
at one time, and so-called scanners, in which each target portion
is irradiated by scanning the pattern through a radiation beam in a
given direction (the "scanning"-direction) while synchronously
scanning the substrate parallel or anti-parallel to this direction.
It is also possible to transfer the pattern from the patterning
device to the substrate by imprinting the pattern onto the
substrate.
It has been proposed to immerse the substrate in the lithographic
projection apparatus in a liquid having a relatively high
refractive index, e.g. water, so as to fill a space between the
final element of the projection system and the substrate. The point
of this is to enable imaging of smaller features since the exposure
radiation will have a shorter wavelength in the liquid. (The effect
of the liquid may also be regarded as increasing the effective NA
of the system and also increasing the depth of focus.) Other
immersion liquids have been proposed, including water with solid
particles (e.g. quartz) suspended therein.
However, submersing the substrate or substrate and substrate table
in a bath of liquid (see, for example, United States patent U.S.
Pat. No. 4,509,852, hereby incorporated in its entirety by
reference) means that there is a large body of liquid that must be
accelerated during a scanning exposure. This requires additional or
more powerful motors and turbulence in the liquid may lead to
undesirable and unpredictable effects.
One of the solutions proposed is for a liquid supply system to
provide liquid on only a localized area of the substrate and in
between the final element of the projection system and the
substrate (the substrate generally has a larger surface area than
the final element of the projection system). One way which has been
proposed to arrange for this is disclosed in PCT patent application
publication WO 99/49504, hereby incorporated in its entirety by
reference. As illustrated in FIGS. 2 and 3, liquid is supplied by
at least one inlet IN onto the substrate, preferably along the
direction of movement of the substrate relative to the final
element, and is removed by at least one outlet OUT after having
passed under the projection system. That is, as the substrate is
scanned beneath the element in a -X direction, liquid is supplied
at the +X side of the element and taken up at the -X side. FIG. 2
shows the arrangement schematically in which liquid is supplied via
inlet IN and is taken up on the other side of the element by outlet
OUT which is connected to a low pressure source. In the
illustration of FIG. 2 the liquid is supplied along the direction
of movement of the substrate relative to the final element, though
this does not need to be the case. Various orientations and numbers
of in- and out-lets positioned around the final element are
possible, one example is illustrated in FIG. 3 in which four sets
of an inlet with an outlet on either side are provided in a regular
pattern around the final element.
One or more unexpected problems may emerge from this new immersion
lithography technology when compared with `dry` lithographic
apparatus that do not have liquid in the exposure radiation path.
On possible problem is that, despite the improved resolution, the
liquid may tend to degrade the image quality in other respects. In
particular, bubbles in the immersion liquid may reduce the quality
of the imaged pattern.
SUMMARY
Accordingly, it would be advantageous, for example, to provide for
de-gassing of a liquid to be used in immersion lithography.
According to an aspect of the invention, there is provided a
lithographic apparatus, comprising:
a semi-permeable membrane;
a liquid inlet adapted to supply liquid to a first side of the
membrane; and
a gas inlet adapted to supply to a second side of the membrane
either:
(a) a vapor of the liquid; or
(b) a gas which dissociates when dissolved in the liquid.
According to an aspect of the invention, there is provided a device
manufacturing method, comprising:
transferring a pattern from a patterning device through a liquid
onto a substrate, wherein the liquid was provided on one side of a
semi-permeable membrane and a gas provided on another side of the
semi-permeable membrane, the gas being either a vapor of the liquid
or a gas which dissociates when dissolved in the liquid.
According to an aspect of the invention, there is provided an
apparatus configured to de-gas a liquid, the apparatus
comprising:
a semi-permeable membrane;
a pump configured to provide the liquid to a first side of the
membrane; and
either
(i) a vaporizer configured to provide vapor of the liquid to a
second side of the membrane; or
(ii) a gas inlet configured to provide a gas which dissociates when
dissolved in the liquid and an ion exchanger for the liquid
downstream of the semi-permeable membrane.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of
example only, with reference to the accompanying schematic drawings
in which corresponding reference symbols indicate corresponding
parts, and in which:
FIG. 1 depicts a lithographic apparatus according to an embodiment
of the invention;
FIGS. 2 and 3 depict a liquid supply system for use in a
lithographic projection apparatus;
FIG. 4 depicts a further liquid supply system for use in a
lithographic projection apparatus;
FIG. 5 depicts another liquid supply system for use in a
lithographic projection apparatus;
FIG. 6 depicts an apparatus for de-gassing a liquid according to an
embodiment of the invention; and
FIG. 7 illustrates another apparatus for de-gassing a liquid
according to an embodiment of the invention.
DETAILED DESCRIPTION
FIG. 1 schematically depicts a lithographic apparatus according to
one embodiment of the invention. The apparatus comprises: an
illumination system (illuminator) IL configured to condition a
radiation beam B (e.g. UV radiation or DUV radiation). a support
structure (e.g. a mask table) MT constructed to support a
patterning device (e.g. a mask) MA and connected to a first
positioner PM configured to accurately position the patterning
device in accordance with certain parameters; a substrate table
(e.g. a wafer table) WT constructed to hold a substrate (e.g. a
resist-coated wafer) W and connected to a second positioner PW
configured to accurately position the substrate in accordance with
certain parameters; and a projection system (e.g. a refractive
projection lens system) PS configured to project a pattern imparted
to the radiation beam B by patterning device MA onto a target
portion C (e.g. comprising one or more dies) of the substrate
W.
The illumination system may include various types of optical
components, such as refractive, reflective, magnetic,
electromagnetic, electrostatic or other types of optical
components, or any combination thereof, for directing, shaping, or
controlling radiation.
The support structure holds the patterning device in a manner that
depends on the orientation of the patterning device, the design of
the lithographic apparatus, and other conditions, such as for
example whether or not the patterning device is held in a vacuum
environment. The support structure can use mechanical, vacuum,
electrostatic or other clamping techniques to hold the patterning
device. The support structure may be a frame or a table, for
example, which may be fixed or movable as required. The support
structure may ensure that the patterning device is at a desired
position, for example with respect to the projection system. Any
use of the terms "reticle" or "mask" herein may be considered
synonymous with the more general term "patterning device."
The term "patterning device" used herein should be broadly
interpreted as referring to any device that can be used to impart a
radiation beam with a pattern in its cross-section such as to
create a pattern in a target portion of the substrate. It should be
noted that the pattern imparted to the radiation beam may not
exactly correspond to the desired pattern in the target portion of
the substrate, for example if the pattern includes phase-shifting
features or so called assist features. Generally, the pattern
imparted to the radiation beam will correspond to a particular
functional layer in a device being created in the target portion,
such as an integrated circuit.
The patterning device may be transmissive or reflective. Examples
of patterning devices include masks, programmable mirror arrays,
and programmable LCD panels. Masks are well known in lithography,
and include mask types such as binary, alternating phase-shift, and
attenuated phase-shift, as well as various hybrid mask types. An
example of a programmable mirror array employs a matrix arrangement
of small mirrors, each of which can be individually tilted so as to
reflect an incoming radiation beam in different directions. The
tilted mirrors impart a pattern in a radiation beam which is
reflected by the mirror matrix.
The term "projection system" used herein should be broadly
interpreted as encompassing any type of projection system,
including refractive, reflective, catadioptric, magnetic,
electromagnetic and electrostatic optical systems, or any
combination thereof, as appropriate for the exposure radiation
being used, or for other factors such as the use of an immersion
liquid or the use of a vacuum. Any use of the term "projection
lens" herein may be considered as synonymous with the more general
term "projection system".
As here depicted, the apparatus is of a transmissive type (e.g.
employing a transmissive mask). Alternatively, the apparatus may be
of a reflective type (e.g. employing a programmable mirror array of
a type as referred to above, or employing a reflective mask).
The lithographic apparatus may be of a type having two (dual stage)
or more substrate tables (and/or two or more support structures).
In such "multiple stage" machines the additional tables or support
structures may be used in parallel, or preparatory steps may be
carried out on one or more tables or support structures while one
or more other tables or support structures are being used for
exposure.
Referring to FIG. 1, the illuminator IL receives a radiation beam
from a radiation source SO. The source and the lithographic
apparatus may be separate entities, for example when the source is
an excimer laser. In such cases, the source is not considered to
form part of the lithographic apparatus and the radiation beam is
passed from the source SO to the illuminator IL with the aid of a
beam delivery system BD comprising, for example, suitable directing
mirrors and/or a beam expander. In other cases the source may be an
integral part of the lithographic apparatus, for example when the
source is a mercury lamp. The source SO and the illuminator IL,
together with the beam delivery system BD if required, may be
referred to as a radiation system.
The illuminator IL may comprise an adjuster AD for adjusting the
angular intensity distribution of the radiation beam. Generally, at
least the outer and/or inner radial extent (commonly referred to as
.sigma.-outer and .sigma.-inner, respectively) of the intensity
distribution in a pupil plane of the illuminator can be adjusted.
In addition, the illuminator IL may comprise various other
components, such as an integrator IN and a condenser CO. The
illuminator may be used to condition the radiation beam, to have a
desired uniformity and intensity distribution in its
cross-section.
The radiation beam B is incident on the patterning device (e.g.,
mask) MA, which is held on the support structure (e.g., mask table)
MT, and is patterned by the patterning device. Having traversed the
patterning device MA, the radiation beam B passes through the
projection system PS, which focuses the beam onto a target portion
C of the substrate W. With the aid of the second positioner PW and
position sensor IF (e.g. an interferometric device, linear encoder
or capacitive sensor), the substrate table WT can be moved
accurately, e.g. so as to position different target portions C in
the path of the radiation beam B. Similarly, the first positioner
PM and another position sensor (which is not explicitly depicted in
FIG. 1) can be used to accurately position the patterning device MA
with respect to the path of the radiation beam B, e.g. after
mechanical retrieval from a mask library, or during a scan. In
general, movement of the support structure MT may be realized with
the aid of a long-stroke module (coarse positioning) and a
short-stroke module (fine positioning), which form part of the
first positioner PM Similarly, movement of the substrate table WT
may be realized using a long-stroke module and a short-stroke
module, which form part of the second positioner PW. In the case of
a stepper (as opposed to a scanner) the support structure MT may be
connected to a short-stroke actuator only, or may be fixed.
Patterning device MA and substrate W may be aligned using
patterning device alignment marks M1, M2 and substrate alignment
marks P1, P2. Although the substrate alignment marks as illustrated
occupy dedicated target portions, they may be located in spaces
between target portions (these are known as scribe-lane alignment
marks). Similarly, in situations in which more than one die is
provided on the patterning device MA, the patterning device
alignment marks may be located between the dies.
The depicted apparatus could be used in at least one of the
following modes:
1. In step mode, the support structure MT and the substrate table
WT are kept essentially stationary, while an entire pattern
imparted to the radiation beam is projected onto a target portion C
at one time (i.e. a single static exposure). The substrate table WT
is then shifted in the X and/or Y direction so that a different
target portion C can be exposed. In step mode, the maximum size of
the exposure field limits the size of the target portion C imaged
in a single static exposure.
2. In scan mode, the support structure MT and the substrate table
WT are scanned synchronously while a pattern imparted to the
radiation beam is projected onto a target portion C (i.e. a single
dynamic exposure). The velocity and direction of the substrate
table WT relative to the support structure MT may be determined by
the (de-)magnification and image reversal characteristics of the
projection system PS. In scan mode, the maximum size of the
exposure field limits the width (in the non-scanning direction) of
the target portion in a single dynamic exposure, whereas the length
of the scanning motion determines the height (in the scanning
direction) of the target portion.
3. In another mode, the support structure MT is kept essentially
stationary holding a programmable patterning device, and the
substrate table WT is moved or scanned while a pattern imparted to
the radiation beam is projected onto a target portion C. In this
mode, generally a pulsed radiation source is employed and the
programmable patterning device is updated as required after each
movement of the substrate table WT or in between successive
radiation pulses during a scan. This mode of operation can be
readily applied to maskless lithography that utilizes programmable
patterning device, such as a programmable mirror array of a type as
referred to above.
Combinations and/or variations on the above described modes of use
or entirely different modes of use may also be employed.
A further immersion lithography solution with a localized liquid
supply system is shown in FIG. 4. Liquid is supplied by two groove
inlets IN on either side of the projection system PL and is removed
by a plurality of discrete outlets OUT arranged radially outwardly
of the inlets IN. The inlets IN and OUT can be arranged in a plate
with a hole in its center and through which the projection beam is
projected. Liquid is supplied by one groove inlet IN on one side of
the projection system PL and removed by a plurality of discrete
outlets OUT on the other side of the projection system PL, causing
a flow of a thin film of liquid between the projection system PL
and the substrate W. The choice of which combination of inlet IN
and outlets OUT to use can depend on the direction of movement of
the substrate W (the other combination of inlet IN and outlets OUT
being inactive).
Another immersion lithography solution with a localized liquid
supply system solution which has been proposed is to provide the
liquid supply system with a liquid confinement structure which
extends along at least a part of a boundary of the space between
the final element of the projection system and the substrate table.
Such a solution is illustrated in FIG. 5. The liquid confinement
structure is substantially stationary relative to the projection
system in the XY plane though there may be some relative movement
in the Z direction (in the direction of the optical axis). See, for
example, U.S. patent application Ser. No. 10/844,575, hereby
incorporated in its entirety by reference. A seal is typically
formed between the liquid confinement structure and the surface of
the substrate. In an embodiment, the seal is a contactless seal
such as a gas seal.
Referring to FIG. 5, reservoir 10 forms a contactless seal to the
substrate around the image field of the projection system so that
liquid is confined to fill a space between the substrate surface
and the final element of the projection system. The reservoir is
formed by a liquid confinement structure 12 positioned below and
surrounding the final element of the projection system PL. Liquid
is brought into the space below the projection system and within
the liquid confinement structure 12. The liquid confinement
structure 12 extends a little above the final element of the
projection system and the liquid level rises above the final
element so that a buffer of liquid is provided. The liquid
confinement structure 12 has an inner periphery that at the upper
end, in an embodiment, closely conforms to the shape of the
projection system or the final element thereof and may, e.g., be
round. At the bottom, the inner periphery closely conforms to the
shape of the image field, e.g., rectangular though this need not be
the case.
The liquid is confined in the reservoir by a gas seal 16 between
the bottom of the liquid confinement structure 12 and the surface
of the substrate W. The gas seal is formed by gas, e.g. air or
synthetic air but, in an embodiment, N.sub.2 or another inert gas,
provided under pressure via inlet 15 to the gap between liquid
confinement structure 12 and substrate and extracted via first
outlet 14. The overpressure on the gas inlet 15, vacuum level on
the first outlet 14 and geometry of the gap are arranged so that
there is a high-velocity gas flow inwards that confines the
liquid.
An embodiment of the present invention relates to an apparatus for
de-gassing a liquid. The apparatus may either be a stand alone
apparatus or coupled to a lithographic projection apparatus. The
de-gasser may be used to de-gas liquids such as photo-resist used
in lithography. However, an embodiment is particularly suited for
de-gassing immersion fluid which will be used in immersion
lithography. In immersion lithography, immersion liquid is
typically positioned between the final element of the projection
system PS and the substrate W.
U.S. patent application Ser. Nos. 10/860,662 and 10/924,192, both
of which are incorporated herein in their entirety by reference,
discuss the use of bubble reduction apparatus to reduce the
occurrence of bubbles in immersion liquid. In these bubble
reduction apparatus, liquid is passed past a semi-permeable
membrane which has pores which the liquid molecules cannot pass
through. In this way the liquid is de-gassed. In an embodiment, the
process is accelerated by applying to the outside of the tubing a
low pressure.
Membranes are used for removal of gasses from liquids in fields
such as microelectronics, pharmaceutical and power applications.
The liquid can be pumped through a bundle of semi-porous membrane
tubing (shown schematically in FIG. 7) using, for example, a pump.
Thus the liquid is de-gassed. The process may be accelerated by
applying to the outside of the tubing a low pressure. Liqui-Cel.TM.
Membrane Contractors available from Membrana-Charlotte, a division
of Celgard Inc. of Charlotte, N.C., USA are suitable for this
purpose and for an embodiment of the present invention as are
Mykrolis Phasor II.RTM. membranes or Fiberflo.RTM. membranes from
Minntech. Membranes which are made of a liquidphobic (e.g.,
hydrophobic) material are advantageous; the pores in the membrane
may be larger than the liquid molecules but, because of the surface
tension of the liquid, they cannot pass the membrane. Such
membranes are typically only suited for use with liquids with a
relatively high surface tension such as water.
A problem with the foregoing method is that the amount of dissolved
gas in the liquid is proportional to the saturation concentration
of the concerned gas in the liquid and the pressure of that gas on
the other side of the semi-permeable membrane. This means that the
gas content which remains in the liquid is proportional to the
saturation level and the applied vacuum level. If on the gas side
of the membrane, a vacuum is applied without or with a very small
gas flow past the membrane, diffusion of the gas out of the liquid
through the membrane will limit the lowest achievable partial
pressure level of the gas at the gas side of the membrane. However,
even with a gas flow, the amount of de-gassing achievable is
limited. In the case of applying a vacuum to one side of the
membrane which is below the vapor pressure of the liquid to be
de-gassed, the semi-permeable membrane is blocked by vapor of the
liquid and so the de-gassing process does not continue. This limits
the level of vacuum which can usefully be used and thereby the
lowest concentration of gas in the liquid.
The examples given below are all for water as the liquid, but an
embodiment of the invention is applicable to any liquid, such as a
top coat. By providing an inert or other stable gas, such as
nitrogen, at ambient pressure on one side of the semi-permeable
membrane, the total gas concentration in parts per billion in the
liquid can be 19000 parts per billion. If an inert or other stable
gas, such as nitrogen, is used with an under-pressure below
atmospheric pressure in the region of 3000 Pa (0.3 atm) (i.e. just
under the vapor pressure of water which is 2700 Pa), for example,
the concentration of gas in the liquid can be reduced to as little
as 578 parts per billion. If a vacuum alone is used (3000 Pa or 0.3
atm), the concentration of gas can be reduced to 727 parts per
billion. However, these levels may not be considered low enough and
an embodiment of the present invention can achieve a total gas
concentration in the liquid of below 200 parts per billion and in
some embodiments lower than 50 or even lower than 5 parts per
billon. As will be appreciated, any under pressure will help reduce
the concentration of gas in the liquid, even 0.95 atm.
An embodiment of the apparatus of the present invention is shown
schematically in FIG. 6. Liquid to be de-gassed is provided to a
inlet 100 and flows past a semi-permeable membrane 120. After being
de-gassed, the liquid proceeds to outlet 140. A chamber 125 may be
provided adjacent the semi-permeable membrane so that liquid spends
more time in the vicinity of the semi-permeable membrane 120. A gas
is provided to inlet 200 and forced to flow past the semi-permeable
membrane 120. The gas continues to exit 240. The gas may either be
allowed to escape to the atmosphere or be re-cycled. The gas can be
provided at an under pressure, at a level at least above the vapor
pressure of the liquid.
In a first embodiment, the gas which is provided on the side of the
semi-permeable membrane 120 opposite to that of the liquid to be
de-gassed is vapor of the liquid to be de-gassed. In this instance,
it is possible to reduce the concentration of gas in the liquid to
below 50 parts per billion. A concentration of 36 parts per billion
is theoretically possible. A typical gas flow rate would be 2
L/minute and a typical liquid flow rate would be 1 L/minute with a
semi-permeable membrane surface area of about 1 m.sup.2, depending
on the level of equilibrium which it is desired to achieve. An
optimal range of flow rate would be between 0.1 and 10 L/minute and
a surface area of the membrane of 0.5 to 5 m.sup.2 could typically
be used.
In this embodiment, it is possible to provide a single liquid inlet
300 which provides liquid to both inlets 100 and 200. A liquid
vaporizer 250 is provided between the inlet 200 and the
semi-permeable membrane 120 to vaporize the liquid. A condenser may
be provided downstream of outlet 240 so that the liquid may be
re-cycled. In an embodiment, the liquid is water.
By using the vapor of the liquid as a sweep gas to de-gas the
liquid, a flow is generated at the gas side of the membrane causing
lower partial pressure gas to be removed from the liquid at the gas
side of the membrane. Because of the lower partial pressure level
at the gas side, the liquid is de-gassed to a significantly lower
level than when a vacuum is applied or a sweep gas is used from a
composition other than the liquid vapor. This means that de-gassing
may be orders of magnitude more effective than using only a vacuum
or an inert or other stable gas as a sweep gas.
In a second embodiment, the gas which is used on the side of the
membrane 120 opposite to the liquid is a gas which dissociates into
ions when dissolved in the liquid. A good example of such a gas is
carbon dioxide (when the liquid is water). A flow of carbon dioxide
is generated on the side of the membrane 120 opposite the liquid
and this causes a significantly lower partial pressure gas to be
removed from the liquid. Thus, by using carbon dioxide under a low
supplied pressure, the partial pressure of all other contaminants
is equal to the supplied pressure times the contamination level in
the carbon dioxide. Thus, the partial pressure of nitrogen in a
carbon dioxide sweep gas at 3000 Pa with 5000 ppm nitrogen is 15
Pa. Because of the lower partial pressure level at the gas side of
the membrane, the liquid is de-gassed to a significantly lower
level than when a vacuum is applied at the gas side. A gas that
dissociates into ions when dissolved in liquid will be absorbed
through the membrane into the liquid, but may later effectively be
removed by means of an ion exchanger 150 which is provided
downstream of outlet 140. The level of de-gassing maybe reduced
even further by applying the carbon dioxide at an under-pressure.
The following table shows the theoretical lowest achievable
equilibrium concentrations under a variety of conditions using
carbon dioxide to de-gas water using a hollow Teflon fiber
membrane.
TABLE-US-00001 Pressure Concentration of gas in Gas (atm) liquid
(ppb) Liquid vapor 0.03 36 CO.sub.2 (5000 ppm purity) 1 121
CO.sub.2 (5000 ppm purity) 0.03 3.6 CO.sub.2 (80 ppm purity) 1 0.48
CO.sub.2 (80 ppm purity) 0.03 0.015
The results in Table 1 are calculated on the basis of an infinite
semi-permeable membrane contact area.
A further refinement of an embodiment of the apparatus according to
the invention is illustrated in FIG. 7 in which like reference
numerals indicate similar objects to those in FIG. 6 and in which
it can be seen that a plurality of tubes are provided, all of which
are made of a semi-permeable membrane. This is one way of
increasing the surface area of the semi-permeable membrane and
therefore the efficiency of the de-gassing process.
In European Patent Application No. 03257072.3, the idea of a twin
or dual stage immersion lithography apparatus is disclosed. Such an
apparatus is provided with two tables for supporting a substrate.
Leveling measurements are carried out with a table at a first
position, without immersion liquid, and exposure is carried out
with a table at a second position, where immersion liquid is
present. Alternatively, the apparatus has only one table.
Although specific reference may be made in this text to the use of
lithographic apparatus in the manufacture of ICs, it should be
understood that the lithographic apparatus described herein may
have other applications, such as the manufacture of integrated
optical systems, guidance and detection patterns for magnetic
domain memories, flat-panel displays, liquid-crystal displays
(LCDs), thin-film magnetic heads, etc. The skilled artisan will
appreciate that, in the context of such alternative applications,
any use of the terms "wafer" or "die" herein may be considered as
synonymous with the more general terms "substrate" or "target
portion", respectively. The substrate referred to herein may be
processed, before or after exposure, in for example a track (a tool
that typically applies a layer of resist to a substrate and
develops the exposed resist), a metrology tool and/or an inspection
tool. Where applicable, the disclosure herein may be applied to
such and other substrate processing tools. Further, the substrate
may be processed more than once, for example in order to create a
multi-layer IC, so that the term substrate used herein may also
refer to a substrate that already contains multiple processed
layers.
Although specific reference may have been made above to the use of
embodiments of the invention in the context of optical lithography,
it will be appreciated that the invention may be used in other
applications, for example imprint lithography, and where the
context allows, is not limited to optical lithography. In imprint
lithography a topography in a patterning device defines the pattern
created on a substrate. The topography of the patterning device may
be pressed into a layer of resist supplied to the substrate
whereupon the resist is cured by applying electromagnetic
radiation, heat, pressure or a combination thereof. The patterning
device is moved out of the resist leaving a pattern in it after the
resist is cured.
The terms "radiation" and "beam" used herein encompass all types of
electromagnetic radiation, including ultraviolet (UV) radiation
(e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm)
and extreme ultra-violet (EUV) radiation (e.g. having a wavelength
in the range of 5-20 nm), as well as particle beams, such as ion
beams or electron beams.
The term "lens", where the context allows, may refer to any one or
combination of various types of optical components, including
refractive, reflective, magnetic, electromagnetic and electrostatic
optical components.
While specific embodiments of the invention have been described
above, it will be appreciated that the invention may be practiced
otherwise than as described. For example, the invention may take
the form of a computer program containing one or more sequences of
machine-readable instructions describing a method as disclosed
above, or a data storage medium (e.g. semiconductor memory,
magnetic or optical disk) having such a computer program stored
therein.
One or more embodiments of the invention may be applied to any
immersion lithography apparatus, in particular, but not
exclusively, those types mentioned above and whether the immersion
liquid is provided in the form of a bath or only on a localized
surface area of the substrate. A liquid supply system as
contemplated herein should be broadly construed. In certain
embodiments, it may be a mechanism or combination of structures
that provides a liquid to a space between the projection system and
the substrate and/or substrate table. It may comprise a combination
of one or more structures, one or more liquid inlets, one or more
gas inlets, one or more gas outlets, and/or one or more liquid
outlets that provide liquid to the space. In an embodiment, a
surface of the space maybe a portion of the substrate and/or
substrate table, or a surface of the space may completely cover a
surface of the substrate and/or substrate table, or the space may
envelop the substrate and/or substrate table. The liquid supply
system may optionally further include one or more elements to
control the position, quantity, quality, shape, flow rate or any
other features of the liquid.
The descriptions above are intended to be illustrative, not
limiting. Thus, it will be apparent to one skilled in the art that
modifications may be made to the invention as described without
departing from the scope of the claims set out below.
* * * * *